In fluid pumping devices requiring the assembly of two or more components together, static seals may be utilized to prevent unwanted fluid leakage or flow at the interface between assembled components. Moreover, such fluid pumping devices may include internal regions that need to be maintained at a certain pressure or at least without the loss of pressure. Static seals may be utilized to prevent fluid leakage and pressure loss. Fluid pumping devices utilizing static seals include Ventricular Assist Devices (VADs), which are utilized as circulatory support devices for patients during or after open heart surgery or as a bridge to heart transplant for cardiac-failure patients. Other circulatory support devices include rotary blood pumps and axial blood pumps.
Typically, circulatory support devices include some type of a pumping unit, or components configured to provide a pumping action, contained in a suitable enclosure. The pumping unit of the circulatory support device may be connected to a patient's heart via cannulae attached to the heart at appropriate locations according to known surgical practices. Particularly in the case of a VAD, the pumping unit may include a flexible blood sac for supporting or replacing heart activity. The blood sac may be attached to an input cannula via a one-way input valve and to an output cannula via a one-way output valve. The enclosure for the blood sac may be provided in the form of two half shells that are coupled together to enclose the blood sac, resulting in an assembled VAD. A sealing element is included at the interface of the two half shells to hermetically seal the interior (containing the blood sac) from the environment external to the assembled VAD. The sealing element is typically constructed from a deformable material, while the half shells are rigid. Upon coupling the half shells together with the deformable sealing element therebetween, the half shells exert pressure on the sealing element. Consequently, the sealing element is compressed and essentially fills in (or conforms to) the interface between the half shells, thereby establishing a static seal. In the case where a flexible blood sac is employed as the pumping unit, one of the half shells may provide a fitting configured for connection to a pneumatic drive unit. The pneumatic drive unit may be operated to provide air or other gas to the interior of the enclosure in pulses (or fluctuating levels of pressure). In response to a pulse of air input, the blood sac is compressed (e.g., collapses, contracts, etc.), thereby pumping blood residing within the blood sac through the output cannula. Between pulses, the blood sac relaxes or expands to enable blood to fill the blood sac from the input cannula.
FIG. 1 is an exploded perspective view of a VAD 100 as described in U.S. Pat. No. 7,217,236, commonly assigned to the assignee of the present disclosure and incorporated herein by reference in its entirety into this application. The VAD 100 includes a disposable pumping unit 120 housed within a reusable pump shell 112. The pumping unit 120 includes a disposable blood sac 122 having an inlet 132 and outlet 134 respectively attached to a disposable one-way inlet valve 126 and outlet valve 124. Tubing connectors 130 and 128 are respectively attached to the inlet valve 126 and outlet valve 124 as interfaces to cannulae (not shown). The pump shell 112 includes an upper clamshell half 114 and a lower clamshell half 116. When assembled together, the upper clamshell half 114 and the lower clamshell half 116 define a pump chamber 142 in which the blood sac 122 resides. The lower clamshell half 116 has an air inlet 138 for connection to a pneumatic drive unit (not shown). The pneumatic drive unit provides a pulsed flow of air to the pump chamber 142 via the air inlet 138, thereby alternating the air pressure in the pump chamber 142 between high and low levels. In response, the blood sac 122 alternately contracts and expands such that blood is pumped along a flow path from the input tubing connector 130, to the inlet valve 126, the interior of the blood sac 122, the outlet valve 124, and to the output tubing connector 128.
In the VAD 100 illustrated in FIG. 1, a static, hermetic seal is formed at least in part by a disposable sealing element 118. The sealing element 118 is located along the plane of the interface between the upper clamshell half 114 and the lower clamshell half 116. Stated in another way, the sealing element 118 is located at the assembly plane of the two-piece pump shell 112 where the respective assembly faces of the upper clamshell half 114 and the lower clamshell half 116 meet. The configuration of the VAD 100, however, makes the ability of this sealing element 118 to consistently provide a hermetic seal at the assembly plane without pressure loss challenging. The configuration of the VAD 100 is characterized by the inlet and outlet fluidic lines being located on the same assembly plane as the faces of the upper clamshell half 114 and the lower clamshell half 116. Thus, as shown in FIG. 1, the inlet 132 and outlet 134 of the blood sac 122, the inlet valve 126 and the outlet valve 124, the tubing connectors 130 and 128, and the input and output cannulae (not shown) are all positioned essentially at the assembly plane between the upper clamshell half 114 and the lower clamshell half 116. Moreover, the tubing connectors 130 and 132 are located proximate to each other on the same side of the VAD 100.
Generally, this configuration for the VAD 100 may be considered as optimal for a variety of reasons. For instance, a surgeon can easily visualize and remember which tubing connectors 130 and 132 are being utilized for the input and output directions of blood flow, respectively. If the cannulae are initially connected to the wrong tubing connectors 130 and 132, the surgeon can easily switch the connections. Moreover, the inputs and outputs to the device are easily observable in one location to determine whether the blood sac 122 or one of the valves 124 and 126 has failed. In addition, assembly and disassembly of the VAD 100 for the purpose of replacing the blood sac 122 or the valves 124 and 126 is thought to be facilitated by this configuration. Ease of assembly and disassembly is particularly important during surgery. However, the configuration illustrated in FIG. 1 requires complex geometry, particularly with regard to various surfaces within the interior of the VAD 100. The valves 124 and 126 and tubing connectors 128 and 130 are accommodated by a cylindrical inlet region 146, a cylindrical outlet region 144, and associated grooves, surfaces, edges, and the like. The pump chamber 142 to be hermetically sealed is in open communication with the inlet region 146 and the outlet region 144. The location of the inlet region 146 and the outlet region 144 are such that there are essentially breaks in the assembly plane of the VAD 100. The sealing element 118 cannot adequately seal the inlet region 146 and the outlet region 144. Thus, hermetic sealing of the interior of the VAD 100 relies in part on securing the tubing connectors 128 and 130 to the upper clamshell half 114 and lower clamshell half 116 at locations such as annular shoulders 137 and the like.
In addition, the configuration illustrated in FIG. 1 requires that the assembly faces of the upper clamshell half 114 and lower clamshell half 116 be parallel to ensure pressure is imparted to the sealing element 118 uniformly. This parallelism limits the range of design options for the VAD 100 and results in the VAD 100 being larger and bulkier than necessary, which is particularly disadvantageous when the VAD 100 is intended to be implantable in the patient.
In addition, the blood sac 122, valves 124 and 126 and the cannulae connected to the valves 124 and 126 via the tubing connectors 130 and 132 are all constructed from a flexible material such as silicone rubber. Hence, these components are unstable during the handling and manipulation required for assembling the components together prior to enclosing them between the upper and lower clamshell halves 114 and 116. Once filled with fluid, these components are easy to deform, making proper handling and manipulation even more difficult.
Therefore, there is a need for providing a fluid pumping device that provides an improved static seal. There is also a need for providing a fluid pumping device that does not require parallel assembly faces and that is easier to assemble and disassemble. Further, there is a need for improving the stability of a fluid pumping device during assembly and disassembly.